Added deletePipeline() (#313).

Author: gmessner

src/main/java/org/gitlab4j/api/PipelineApi.java

@@ -227,6 +227,19 @@ public Pipeline createPipeline(Object projectIdOrPath, String ref) throws GitLab
         return (response.readEntity(Pipeline.class));
     }
 
+    /**
+     * Delete a pipeline from a project.
+     *
+     * <pre><code>GitLab Endpoint: DELETE /projects/:id/pipelines/:pipeline_id</code></pre>
+     *
+     * @param projectIdOrPath the project in the form of an Integer(ID), String(path), or Project instance
+     * @param pipelineId the pipeline ID to delete
+     * @throws GitLabApiException if any exception occurs during execution
+     */
+    public void deletePipeline(Object projectIdOrPath, int pipelineId) throws GitLabApiException {
+       delete(Response.Status.ACCEPTED, null, "projects", getProjectIdOrPath(projectIdOrPath), "pipelines", pipelineId);
+    }
+
     /**
      * Retry a job in specified pipelines in a project.
      *